The present invention relates to a two-circuit pressure regulator, the two circuits of which each have an inlet for connection to a pressure source, especially for connection to a different circuit of a tandem master brake cylinder of a motor vehicle, an outlet for connection to a pressure consumer, especially for connection to a different wheel brake cylinder of a motor vehicle, a pressure regulator valve connected between inlet and outlet loaded in the opening direction by a spring and which closes when a predetermined switching pressure is reached and with a further pressure increase in the inlet port influences the pressure in the outlet port according to a predetermined control action. The two regulator valves are separated from one another by a leak indication piston, slideably guided in a housing bore of the two-circuit pressure regulator and receiving on opposite end surface thereof the pressure in the inlet or outlet port of both circuits. The leak indication piston is axially shifted in one of the two circuits relative to the other of the two circuits when a pressure drop occurs in either of the two circuits and operates a leak indication switch.
Two-circuit pressure regulators of this type are especially used for motor vehicles and serve the purpose of controlling the braking force of individual wheels. Since the rear wheels in particular tend to lock easily during the braking process their braking force must be reduced or limited compared to the braking force of the front wheels. For this purpose each of the wheel brake cylinders of the rear wheels are connected to a different one of the outlets of the two-circuit pressure regulator and each of the inlets of the two-circuit pressure regulator is connected to a different one of the circuits of a tandem master brake cylinder. Each circuit of the tandem master cylinder is also connected to a different one of the wheel brake cylinders of the front wheels.
In the Great Britain Pat. No. 1,495,768 published Dec. 21, 1977, a two-circuit pressure regulator of the type mentioned above is described which works as a pressure reducing device. In this known two-circuit pressure regulator the valve springs of the non-return valves are arranged at the end surfaces of the indication piston, so that the leak indication piston can have, with equal pressure in both circuits, a stable position. Since, however, during operation unavoidable slight pressure differences occur in both circuits the leak indication piston is constantly pushed to and fro slightly so that the leak indication switch may be operated without a real leak existing and the springs of the non-return valves are unequally loaded. Furthermore, the construction and assembly of this known two-circuit pressure regulator are relatively expensive.